Li ZHANG, Li ZHANG, Hong LIAO,Hong LIAO, and Jianping LI and Jianping LI

Institute of Atmospheric PhysicsChinese Academy of Sciences

Impacts of Asian Summer Monsoon on Seasonal and Interannual Variations of

Aerosols over Eastern China

Motivations

China has high concentrations of aerosols

--- Domestic air quality --- Outflow of air pollutants --- Climatic effects

China is located within a large monsoon domain

--- Seasonal variations in meteorological fields associated with Asian summer monsoon can influence transport, deposition, and chemical reactions of aerosols;

--- Asian summer monsoon has interannual and decadal variations (it has been weakening since 1970s).

Change in Asian summer monsoon is the most important aspect of climate change in China

--- This work is the first step of our study for understanding the effect of climate change on air quality in China

War

m m

ois

t

Summer monsoonMay - September

Col

d d

ry

Winter monsoonNovember - March

Asian Monsoon

Somali JetSomali Jet

Rainfall/MeiyuRainfall/Meiyu

DeepDeepconvectionconvection

South Asian HighSouth Asian High

Subtropical HighSubtropical High

Asian Summer MonsoonAsian Summer Monsoon

Simulated Surface-layer PM2.5 Concentrations (μg m-3)

for ordinary monsoon year 2001

JAN

JUL OCT

APR

• Model version : GEOS–Chem 7.3.6 • Resolution: 4° x 5°; 30 vertical layers• Meteorology: NASA GEOS-3 (Jan 1~Dec 31, 2001)• David Streets 2006 emissions inventory

Simulated Seasonal Variations of Aerosols

Agree with Measurements

Chao et al., 2007

Eastern China

0

4

8

12

16

20

24

28

32J AN APR

J UL OCT

PMPM2.52.5 NONO33-- SOSO44

2-2- NHNH44++ BCBC OCOC

110-120E, 20-45N

Winter

Summer

Debell et al., 2006

Western U. S.

Eastern U. S.

The IMPROVE Measurements of Fine Aerosol Species

Seasonal Variation in China is Opposite to That in the US

JJA stream lines and wind velocity (colors) at 925 mb

Time-longitude distribution of meridional wind averaged over 5 ̊ S - 5 ̊ N

Major Factors that Influence Seasonal Variation of Aerosols in China:

(1) Four channels of cross-equatorial flows associated with Asian summer monsoon bring clean air to China

40-65E (First channel, Somali jet) 85-95E (Second channel)

105-115E (Third channel) 120-135E (Fourth channel)

Correlation between Ic (Wind) of Each Channel and PM2.5

Large wet deposition starting from mid-June contributes to a sudden decrease in PM2.5 in eastern China

109 kg/dayMay 31 – June 4

June 20-24June 15-19

June 10-14June 5-9

June 25-29

Major Factors that Influence Seasonal Variation of Aerosols in China:

(2) Large Rainfall Associated with Asian Summer Monsoon

0

2

4

6

8

1 2 3 4 5 6 7 8 9 10 11 12

0

0. 5

1

1. 5

2

1 2 3 4 5 6 7 8 9 10 11 12

0

4

8

12

16

20

24

1 2 3 4 5 6 7 8 9 10 11 120

2

4

6

8

10

1 2 3 4 5 6 7 8 9 10 11 12

0

1

2

3

4

5

1 2 3 4 5 6 7 8 9 10 11 12

0

0. 5

1

1. 5

2

2. 5

3

1 2 3 4 5 6 7 8 9 10 11 12

PMPM2.52.5SOSO44

2-2-

NONO33-- NHNH44

++

BCBC OCOC

Control run: with seasonal emissions

JANEmis:emissions set to Jan. values

JULEmis: emissions set to July values

Effect of Monsoon is Much Larger than the Effect of Seasonal Variation in Emissions

-59.3%

-58.4%

PM2.5(JUL) - PM2.5(JAN)

PM2.5(JAN)

-63.7%Control run:

JANEmis:

JULEmis:

Asian Summer Monsoon Index(represents the strength of monsoon)

(b)

East Asia Summer Monsoon； 1040 110140

South Asia Summer monsoon； 2.520N, 70110E

Li and Zeng (2002, 2003, 2005)

1998: Weakmonsoon year

2002: Strongmonsoon year

August

July

June

PM2.5 OC Sulfate

Averaged over eastern China, surface PM2.5 concentrations in the weak monsoon year 1998 is higher than that in the

strong monsoon year 2002 by 44.6%

Differences in Surface-layer Aerosol Concentrations between the Weak Monsoon Year 1998 and the Strong Monsoon Year 2002

Differences in Meteorological Fields Between the Weak Monsoon year 1998 and Strong Monsoon Year 2002

June

August

July

Precipitation and 850-hPa winds (1998-2002)

925hPa meridional winds(1998-2002)

Weaker cross-equatorial flows brought less clean air to China

Abnormal winds did not favor the outflow of pollutants in weak monsoon year

Higher aerosol conc. in the weak monsoon year 1998, because of

Factors influence seasonal variation of aerosols in eastern China:

With Asian summer monsoon, PM2.5 concentrations in eastern China in July is lower than those in January by about 60%;

Average summer surface PM2.5 concentration in eastern China in the weak monsoon year 1998 is higher than that in the strong monsoon year 2002 by 44.6%. The difference in concentration can mostly be explained by the difference in transport (winds).

SUMMARY

--- Cross-equatorial flows from the Southern Hemisphere bring clean air to eastern China;--- Rainfall associated with summer monsoon leads to large wet deposition of aerosols

Acknowledgements: Support from China NSF #90711004 and #40775083